This is off IMDB.com's triva section for the show.
"Each episode's title card is accompanied with audio containing only Morse code (dots and dashes, or short and long beeps) which, when translated, provides a short hint (around 3 words) about the episode to come."
"The Morse code that accompanies the opening credits of each episode is broadcast at 15 words per minute at 1000 Hz frequency."